Ventilation System for a Perishable Goods Store

ABSTRACT

The present invention provides a ventilation system for a perishable goods store and a method of operating a ventilation system for a perishable goods store. The system of the present invention may monitor and control the temperature and humidity of the goods within the store and comprises a controller for automatically operating the system, a duct through which air is propelled into the store, pressure control means for controlling the pressure within the duct and a pressure monitoring means for measuring the pressure within the duct. The controller monitors the pressure within the duct and controls the pressure control means ensure the air pressure within the duct is maintained within a defined pressure range. The pressure control means may comprise at least one variable speed fan. The present invention is advantageous in that it optimises the back-pressure within the duct, against which the at least fan must act, thereby providing a more efficient ventilation system.

FIELD OF THE INVENTION

The present invention relates to the storage of perishable goods andprovides a ventilation system for a perishable goods store and a methodof operating a ventilation system for a perishable goods store.

BACKGROUND TO THE INVENTION

Perishable goods are often stored in large quantities within stores. Thestorage of perishable goods requires control of the environmentalconditions in which those goods are stored. For example, in order tomaintain the lifespan and quality of many food items it is necessary tostore those items within certain humidity and/or temperature limits.Therefore, stores are typically large purpose built or suitably modifiedbuildings that include a ventilation system in order to provide thenecessary conditions. A ventilation system may only control the humiditywithin a store and not the temperature. Similarly, a ventilation systemmay only control the temperature within in a store and not the humidity.However, most ventilation systems control both the temperature andhumidity within a store and are heating and ventilation systems.

There are two main types of storage for perishable goods: bulk storageand box storage. In bulk storage the items are simply stored loosewithin the store, while in box storage the items are stored within boxesthat are then stacked within the store. Heating and ventilation systemsfor both of these types of stores operate in substantially the samemanner, as described below.

A typical heating and ventilation system of a perishable goods storecomprises at least one fan located within a fan housing, at least oneheater also located within the fan housing and exhaust louvers locatedaround the store. The fan housing has a closable air inlet to theoutside of the store such that air may be drawn in from the surroundingswhen the inlet is open. Furthermore, the fan housing is formed such itmay draw air in from the store when the air inlet is closed. To achievethis the fan housing may also have a second closable air inlet to theinterior of the store or may be formed such that when the air inlet tothe outside of the store is closed air is drawn into the housing fromthe interior of the store. A second closeable air inlet may be formed asa recirculation louver. Heating and ventilation systems are normallyautomatically controlled by a controller in order to ensure theconditions within the store remain within defined temperature andhumidity ranges.

The fan or fans of a typical heating and ventilation system can beoperated to recirculate air around the store and/or to draw in air fromthe surroundings. This is done in the following manner. Air is drawninto the fan housing from the surroundings and/or from the interior ofthe store depending upon the degree of opening of the air inlet or airinlets. This air is then blown down a main duct and distributed eitherinto under-floor lateral ducts (in bulk stores) or into plenums aligningthe bases of the boxes (in bulk stores) and then into the crop. Theopening of the exhaust louvers is controlled to allow the amount of airescaping the store through the louvers to be equal to the amount of airbeing drawn into the store from the surroundings so to avoidpressurising the store. For example, if air is only being recirculatedwithin the store the exhaust louvers will be closed. Similarly, if airis only being drawn in from the surroundings the exhaust louvers will beopen.

The amount of air being recirculated and the amount of air being drawnin from the surroundings is controlled by the controller in order toensure the perishable goods are stored within a pre-defined humidityrange. This is done by monitoring humidity within the store and withinthe duct. Generally, a heating and ventilation system will comprise ahumidity sensor positioned within the duct and a number of humidityprobes placed in random positions within the stored goods. The readingof the sensor and the probes is fed to the controller in order toprovide a measure of the humidity within the store and the duct. Thecontroller uses the information from the sensor and the probes tocontrol the ratio of the volume of air that is recirculated within astore to the volume of air that is drawn into the store from thesurroundings by controlling the degree of opening of the air inlet orair inlets of the fan housing. At the same time, the degree of openingof the exhaust louvers is controlled in order to ensure that the storeis not pressurised. Generally, if the humidity within the store is toohigh the amount of air drawn in from the surroundings will be increasedand the amount of air recirculated about the store will be reduced inorder to reduce the humidity. Similarly, if the humidity within thestore is too low the amount of air drawn in from the surroundings willbe reduced and the amount of air recirculated about the store will beincreased in order to increase the humidity. This is, of course,dependent upon the humidity of the air surrounding the store. When theair surrounding the store is more humid than this the heater or heatersmay be used to reduce the humidity of the air drawn from thesurroundings before it is blown into the store. The degree to which thesurrounding air can be dried by the heaters depends upon the temperaturedifference between the set store temperature (as discussed below) andthe temperature of the surrounding air. In particular, if the heatersare not operating to heat the store the heaters can be set to heat theair to or below the set store temperature to reduce the humidity of theinlet air. However, this is dependent upon the air surrounding the storealso being below the set store temperature. In order to monitor thehumidity outside the store a heating and ventilation system may furthercomprise external humidity monitoring means e.g. one or more externalhumidity sensors.

The heater or heaters are controlled to maintain the temperature withina store. Specifically, the heater or heaters are turned on when the airtemperature within the store duct falls below a set duct temperaturesuch that air being propelled into the store via the duct is heated toat least this set duct temperature. The set duct temperature ensuresthat excessively cold air is not blown into the store. The heater orheaters are also turned on when the temperature within the store fallsbelow a set store temperature such that air being propelled into thestore via the duct is heated to the set store temperature. When thetemperature within the duct exceeds the set duct temperature and thetemperature within the store exceeds the set store temperaturetemperature the heaters are turned off. Generally, the temperaturewithin the duct is monitored by means of a temperature sensor placed inthe duct and the temperature within the store is monitored by a numberof temperature probes placed within the crop in random positions. Theset store temperature and the set duct temperature may be the same orthe set duct temperature may be lower than the set store temperature.

In order to distribute heat evenly throughout a store, when the heateror heaters are operating the fan or fans are also operated, even if thehumidity within the store is within the defined humidity range. However,if the temperature within the store is above the set store temperatureand the temperature within the duct is above the set duct temperaturebut the humidity within the store is outside the limits of the definedhumidity range the fan or fans are operated, as described above, but theheater or heaters are not operated unless they are operated to dry theair entering the store.

Importantly, a heating and ventilation system, as described above,operates to maintain the conditions in the store only within a definedhumidity range and at the set store temperature. The system is used, andthe fan or fans are turned on, only when the humidity falls outside ofthe relevant range or the temperature in the store or duct falls below aset temperature. When the conditions within the store are within thedefined humidity range and the crop is at the set store temperature theheating and ventilation system is not used. It is these defined limitsthat dictate when the fan or fans and heater or heaters are switched onand switched off. For example, typical limits that are used when storingonions are 65% to 75% relative humidity and a set store temperature of27° C.

Store heating and ventilation systems function well in that they allowfor the relatively long-term storage of perishable goods in a climatecontrolled environment. However, they use a lot of power and areexpensive to run. Additionally, due to the intermittent use of highcapacity fans it is often difficult to obtain a uniform temperature andhumidity throughout a store. Furthermore, the fan or fans can generatehigh back pressures within the duct and working against these backpressures can significantly reduce the efficiency of the heating andventilation system Therefore, there is a need for an improved heatingand ventilation system for a store that is more power efficient and thatcan provide a more uniform temperature and humidity distributionthroughout the store.

SUMMARY OF INVENTION

The present invention provides a ventilation system when used with aperishable goods store comprising:

a controller for automatically operating the system;

a duct through which air is propelled into the store;

a pressure monitoring means for measuring the air pressure within theduct; and

pressure control means for controlling the pressure within the duct;

wherein when air is propelled through the duct the controller monitorsthe duct pressure, as measured by the pressure monitoring means, andcontrols the pressure control means to ensure that the air pressurewithin the duct is maintained within a defined pressure range.

The present invention can operate significantly more efficiently thanheating and ventilation systems according to the prior art. Inparticular, the present invention allows the working pressures of aventilation system to be optimised such that the back pressure withinthe duct is at an optimal level and the amount of energy wastedoperating against the back pressure is minimised. Furthermore, thedefined pressure range, and resulting optimal duct pressure, can resultin the air being distributed from the duct into the store moreuniformly.

Preferably, the pressure range for a specific ventilation systemaccording to the present invention is set such that the pressure withinthe duct is optimal for the store. Specifically, the pressure range maybe defined such that the ventilation system works at optimum efficiencyby minimising back-pressure within the duct but still providing good airdistribution, thereby allowing relatively quick adjustments to thetemperature and humidity of the store. Therefore, the defined pressurerange of the present invention that is set is dependent upon thespecific heating and ventilation system and the goods being stored.Generally, the optimum pressure range is dependent upon the power of thesystem, the size of the store and the size and dimensions of the ductand any associated lateral ducts. The goods being stored also affect theoptimum defined pressure range. For example, the tolerance of the goodsto variations in temperature and humidity and the mode of storage (e.g.curing or simple storage) will affect the pressure range. The pressurerange will be between a set upper pressure and a set lower pressure.

In the same manner of as heating and ventilation systems according tothe prior art, air is propelled through the duct and into the store ifthe conditions within the store are outside of the desired parameters,for example if the humidity is outside of the defined range and/or thetemperature is too low. However, when system of the present invention isoperated and the pressure within the duct falls below the set lowerpressure of the pressure range the pressure control means is operated bythe controller to increase the pressure within the duct. Similarly, whenthe system of the present invention is operated and the pressure withinthe duct rises above the set upper pressure of the pressure range thepressure control means is operated by the controller to decrease thepressure within the duct.

The pressure range of the present invention may be automatically set bythe controller based on monitored variables such as the air speedthrough the goods in the store, the power used by the system, the rateof change of humidity and/or temperature within the store and how fullthe store is. Alternatively, the pressure range may be manually inputinto the controller by an operator based upon an assessment of the storeand the heating and the ventilation system. Preferably, the controllerof the present invention allows manual and automatic alteration of thepressure range during operation of the ventilation system in order tooptimise that operation. Manual and/or automatic alteration of thepressure range may be used to ensure there is good air flow through thecrop.

A ventilation system according to the present invention will typicallyrun slower and longer than heating and ventilation systems according tothe prior art wherein the air pressure within the duct is disregardedand the system is simply turned on or off when necessary without anycontrol of the pressure within the duct. Despite running longer thanprior art ventilation systems, the present invention may providesignificantly higher energy efficiency and improved air distribution

The pressure control means of the present invention may comprise atleast one variable speed fan for propelling air through the duct andinto the store. By controlling the speed of the variable speed fan thepressure within the duct may be controlled. Specifically, by increasingthe speed of the at least one variable speed fan air will be propelledinto the duct at a higher rate thereby increasing the pressure withinthe duct and by decreasing the speed of at least one variable speed fanair will be propelled into the duct at a lower rate thereby decreasingthe pressure within the duct.

The pressure control means of the present invention may comprise aplurality of fans for propelling air through the duct into the store. Byoperating the plurality of fans individually the pressure within theduct may be controlled. Specifically, when the system is operated atleast one of the fans will be switched on and the remainder of theplurality of fans may be individually switched on or off to increase ordecrease or the pressure within the duct respectively.

If the pressure control means does comprise a plurality of fans the fansmay be operated substantially independently by the controller.Alternatively, it may be preferable that the controller controls thefans to operate in series. That is, when it is necessary to increase thepressure within the duct an additional fan is switched on when all thecurrently operating fans are operating at maximum speed, rather thanoperating all of the fans simultaneously and increasing their operatingspeed. Similarly, when it is necessary to reduce the pressure within theduct individual fans are switched off in turn, rather than operating allof the fans but reducing their operating speed. The skilled person willappreciate that a plurality of fans can be operated in this mannerwhether they are fixed speed fans, variable speed fans or a mixture ofboth types.

If the system of the present invention comprises a plurality of fansthose fans may be arranged in any manner that is apparent to the personskilled in the art. For example, the fans may be arranged in series inthe direction in which air is propelled such that the propelled airpasses through each fan. Alternatively, the fans may be positionedsubstantially adjacent to one another.

It is to be understood that if the present invention comprises aplurality of fans those fans may all be variable speed fans or theplurality of fans may all be fixed speed fans or the plurality of fansmay comprise a mixture of fixed and variable speed fans. Any fan of thepresent invention may be an axial fan or a centrifugal fan or any othertype of suitable fan. If the system comprises a plurality fans they mayall be the same type of fan or may be a mixture of types of fan. As willbe understood by the person skilled in the art, the number and type offans will be largely dependent upon engineering considerations includingenergy efficiency, the volume of air required per tonne of crop, thesize of the store, the goods that are being stored, the size of theduct, the available power supply and the size of any housing in whichthe at least one fan is housed.

Additionally or alternatively, the pressure control means of the presentinvention may comprise controllable openings from the duct. Theseopenings may lead from the duct into lateral ducts (in a bulk store) orinto plenums (in a box store). By controlling the degree of opening ofthe openings the pressure within the duct may be controlled.Specifically, by increasing the degree of opening of the openings thepressure within the duct may be decreased as air will be allowed toescape from the duct at a higher rate and by decreasing the degree ofopening of the openings the pressure within the duct may be increased asair will be allowed to escape from the duct at a lower rate.

The present invention may be used in storing any perishable good. Thepresent invention may be used for the long-term storage of food itemssuch as root vegetables e.g. onions, potatoes, red beet etc.

The pressure monitoring means may be any means that is suitable formonitoring the pressure within the duct. Preferably, the pressuremonitoring means is a pressure sensor positioned within the duct aboutone third of the length of the duct from the at least one fan.Positioning an air pressure sensor at this position within the ductprovides the best measure of the back pressure within the duct. However,it is to be appreciated that the pressure in the duct may be monitoredat any point within the duct and/or at more than one point within theduct.

As will be understood by the person skilled in the art, the controlmeans of the present invention may be a computer control unit that is inelectronic communication with the components of the ventilation system.The control unit may be automatic. Additionally, the controller mayinclude manual input means for allowing an operator to vary theoperation of the heating and ventilation system. The manual input meansmay allow an operator to vary the operation of the system for thespecific goods being stored or the storing regime being operated (e.g.curing or storing) or for any other storing variable.

The present invention may further comprise a plurality of air speedprobes positioned within the goods stored within the perishable goodsstore for monitoring the air speed through the goods. The informationfrom the air speed probes may be used to ensure that air is beingcirculated through all of the goods within the store. Additionally oralternatively, information from the air speed probes may be used tocontrol the system. For example, the controller may operate the systemto ensure is a specific minimum average air speed through the goods. Theair speed probes may be positioned randomly throughout the goods or theymay be positioned at regular intervals throughout the goods.

Preferably, the present invention further comprises a fan housing inwhich any fan is housed. The fan housing may be substantially externalto the store, substantially internal to the store or formed as part ofthe structure of the store. Advantageously, the fan housing willcomprise a closeable air inlet that allows air to be drawn into thehousing from the surroundings when air inlet is open and wherein the fanhousing may draw air into the housing from within the store when the airinlet is closed. This may be achieved by having a second air inlet tothe interior of the store. The second air inlet may be a recirculationlouver. It is to be understood that, alternatively to having a closeableair inlet to the surrounding formed as part of the housing, a closeableair inlet to the surroundings may be provided away from, but incommunication with, the fan housing.

Preferably, the present system may form part of an otherwiseconventional heating and ventilation system according to the prior art.In particular, the system of the present invention may include any orall of the following features: humidity monitoring means for monitoringthe humidity within the store, humidity monitoring means for monitoringthe humidity outside of the store, at least one heater, temperaturemonitoring means for monitoring the temperature within the store. It isto be noted that a ventilation system according to the present inventionmay be a ventilation only system that does not monitor or control thetemperature within the store. Such a system would not comprisetemperature monitoring means or at least one heater. Similarly, aventilation system according to the present invention may be a heatingand ventilation system that monitors and controls the temperature withinthe store but does not monitor or control the humidity within the store.Such a system would not comprise any humidity monitoring means.Preferably the system of the present invention is a heating andventilation system and is capable of monitoring and controlling both thehumidity and temperature within a store.

If a system according to the present invention does monitor and controlthe humidity within the store the humidity monitoring means formonitoring the humidity within the store may comprise a humidity sensorpositioned within the duct and/or a plurality of humidity probespositioned within the perishable goods within the store. Such a iscontrolled to operate when the humidity within the store is outside of adefined humidity range such that the humidity within the store iscorrected to within the defined range in the same manner as the priorart.

Similarly, if a system according to the present invention is a heatingand ventilation system and monitors and controls the temperature withinthe store the temperature monitoring means for monitoring thetemperature within the store may comprise a temperature sensorpositioned within the duct and/or a plurality of temperature probespositioned within the perishable goods within the store. Such a system,including the at least one heater, would be controlled to operate andthereby raise the temperature within the store when the temperaturewithin the store is below a set store temperature in the same manner asthe prior art. The at least one heater of a heating and ventilationsystem according to the present invention may be a modulating burner.

It is to be understood that the system of the present invention may beused in the same manner as heating ventilation systems according to theprior art for storing goods for extended periods at a constanttemperature and within a constant humidity range or for storing goodswithin controlled but varying conditions. For example, the system of thepresent invention may be used for cooling products after an extendedperiod of curing. This can be done by reducing the store set temperatureand the store duct temperature at a controlled rate such that the goodswithin the store are cooled.

A system according to the present invention may further comprise datastorage means for recording data from any monitoring means and forrecording when and how the components of the system are operated. Thisis beneficial as analysis of the recorded data may allow optimisation ofthe system. Furthermore, recorded data is beneficial should the system,for any reason, fail to properly control the environmental conditionswithin the store, as a failure analysis may then be carried out on thebasis of that data.

Preferably the present invention will comprise a plurality of exhaustmeans located around the store for controlling the exhaust of air fromthe store such that when the system is in use the volume of air beingdrawn into the store is substantially equal to the volume of air leavingthe store. In the same manner as the prior art the exhaust means maycomprise exhaust louvers. Advantageously, the exhaust means areautomatically controlled by the controller when the system is operated.

The present invention also provides a method of operating ventilationsystem of a perishable goods store comprising a duct through which airis propelled into the store, wherein the air pressure within the duct ismonitored and pressure control means are used to control the pressurewithin the duct such that it remains within a defined pressure range.

The method of the present invention is particularly advantageous as itmay enable a ventilation system for a perishable goods store to besignificantly more energy efficient that was previously possible. It isto be understood that the method of the present invention may furthercomprise operating any or all of the features of the system of thepresent invention that are described above. These features may beoperated in the manner described above or in the conventional mannerthat will be immediately apparent to the person skilled in the art.

DRAWINGS

FIG. 1 is a schematic plan view of a bulk onion store including aheating and ventilation system according to the present invention; and

FIG. 2 is a schematic cross-sectional view of the bulk onion store ofFIG. 1.

A bulk onion store 1 is shown in FIGS. 1 and 2. Although a bulk store 1is illustrated it is to be understood that the present invention isequally applicable to box stores. The store 1 has a fan housing 2located substantially external to the store at a first end of the store.The fan housing 2 contains an axial fan 3 and a main duct 4 extends froman inner end of the fan housing along the centre of the store 1. Amodulating burner (not shown) is also positioned within the fan housing2. A plurality of lateral ducts 5 extend laterally outwards from themain duct 4 under a floor 10 of the store 1.

Temperature, humidity and pressure sensors 7 are positioned within themain duct 4 about one-third of the way along the length of the mainduct. Four exhaust louvers 6 are positioned on the side walls of thestore 1 near the top of the store. The store 1 has two loading doors 8,one either side of the main duct 4, at a second end of the storeopposite the fan housing 2. An onion crop 9 is piled on the floor 10 ofthe store 1 either side of the main duct 4. Temperature, humidity, andair speed probes 11 are randomly positioned within the crop 9. The store1 illustrated in FIGS. 1 and 2 is full and the onion crop 9 reaches thetop of the main duct 4 but lies below the level of the exhaust louvers 6such that an air space 12 is provided above the crop 9 and below theroof of the store 1. However, it is to be understood that the store 1need not be full for the heating and ventilation system to operate. Theheating and ventilation system may be operated when the store 1 is onlypartially full or even when the store empty.

The heating and ventilation system of the store 1 comprises the fanhousing 2, the axial fan 3, the modulating burner, the exhaust louvers6, temperature, humidity and air speed probes 11 and the temperature,humidity and pressure sensors 7. All of these components are incommunication with an automatic controller (not shown) of the heatingand ventilation system. The probes 11 and sensors 7 communicate theirtemperature, humidity, pressure and air-speed readings to thecontroller. The controller uses this information to operate the fanhousing 2, the axial fan 3, the modulating burner and the exhaustlouvers 6 appropriately. In particular, the fan housing 2 can becontrolled to allow air to be drawn in from the surroundings and/orallow air to be drawn in from the store 1. Specifically, the fan housing2 includes an air inlet from the surroundings and an air inlet from thestore 1. The degree of opening of these inlets is controlled to controlthe proportion of air drawn into the fan housing 2 from the surroundingsand from the store 1. The axial fan 3 is a variable speed fan and can becontrolled to operate at a suitable speed to draw air in from thesurroundings and/or the store depending upon the state of inlets of thefan housing 2 and propel that air along the main duct 4. When theventilation system of the store is operated, air from the main duct 4 ispropelled through the lateral ducts 5 and passes up through the cropthrough holes formed through an upper side of the lateral ducts 5 andcorresponding holes formed through the floor of the store 1. The degreeof opening of the exhaust louvers 6 is controlled to ensure that thestore is not pressurised and remains at substantially the same pressureas the air pressure outside the store. The flow of air through the store1 is illustrated in the Figures by the broad arrows. The modulatingburner can be operated to heat the air being propelled by the axial fan3 through the main duct 4 in order to heat the store 1. The controllerincludes data logging means which stores the readings from the sensors11 and the probes 7 and records when and how each of the othercomponents is operated over time. The data in the data logging means canbe extracted from the controller by a user in order to analyse theoperation of the heating and ventilation system.

The modulating burner, the fan housing 2 (including the air inlet fromthe surroundings and the air inlet from the store 1) and the exhaustlouvers 6 are operated by the controller in a conventional manner, aswill be immediately understood by the person skilled in the art. Themodulating burner and fan housing 6 are operated to ensure that thehumidity within the store I remains between 65% and 75% relativehumidity and the temperature within the store remains at the store settemperature of 27° C. The axial fan 3 is a variable speed fan and isoperated by the controller in the same manner as the prior art in thatit is operated when the humidity falls outside of the defined rangeand/or the temperature falls below the store set temperature of 27° C.However, when the axial fan 3 is operated the controller monitors theair pressure with the main duct 4, as measured by the sensors 7, and theair speed through the crop 9, as measured by the probes 11. The speed ofthe axial fan 3 is controlled to ensure the optimum pressure within themain duct 4 and a minimum air speed through the crop 9 is attained. Thisis done by maintaining the air pressure within the main duct 4 within adefined range i.e. below a set upper pressure and above a set lowerpressure and by ensuring the air speed through the crop 9 is above aminimum limit. The pressure limits within the main duct 4 depend uponthe axial fan 3 and the dimensions of the main duct 4 and lateral ducts5, as will be understood by the person skilled in the art. Inparticular, it is advantageous to optimise the back pressure actingagainst the operation of the axial fan 3. The minimum air speed throughthe crop 9 is set to ensure good air distribution through the crop 9 andthereby ensure that the whole of the crop is being ventilated.

1. A ventilation system when used with a perishable goods storecomprising: a controller for automatically operating the system, a ductthrough which air is propelled into the store, a pressure monitoringmeans for measuring the air pressure within the duct; and pressurecontrol means for controlling the pressure within the duct; wherein whenair is propelled through the duct the controller monitors the ductpressure, as measured by the pressure monitoring means, and controls thepressure control means to ensure that the air pressure within the ductis maintained within a defined pressure range.
 2. The system accordingto claim 1, wherein the pressure control means comprises at least onevariable speed fan.
 3. The system according to claim 1, wherein thepressure control means comprises a plurality of fans.
 4. The systemaccording to claim 3, wherein the pressure control means comprises aplurality of fans operated in series.
 5. The system according to claim2, wherein the at least one fan is an axial fan.
 6. The system accordingto claim 2, wherein the at least one fan is a centrifugal fan.
 7. Thesystem according to claim 2 further comprising a fan housing in whichthe at least one fan is housed.
 8. The system according to claim 7,wherein the fan housing comprises a closeable air inlet that allows airto be drawn into the housing by the at least one fan from thesurroundings when air inlet is open and wherein the fan housing may drawair into the housing from within the store when the air inlet is closed.9. The system according to claim 1, wherein the pressure control meanscomprises at least one controllable opening from the duct.
 10. Thesystem according to claim 1, wherein the pressure monitoring meanscomprises a pressure sensor positioned about one third of the length ofthe duct from the at least one fan.
 11. The system according to claim 1,further comprising a plurality of air speed sensors positioned withinthe goods stored within the perishable goods store for monitoring theair speed through the goods.
 11. The system according to claim 1,further comprising humidity monitoring means for monitoring the humiditywithin the store.
 12. The system according to claim 11, wherein thehumidity monitoring means comprises a humidity sensor positioned withinthe duct.
 13. The system according to claim 11, wherein the humiditymonitoring means comprises a plurality of humidity probes positionedwithin the perishable goods within the store.
 14. The system accordingto claim 1, further comprising humidity monitoring means for monitoringthe humidity outside the store.
 15. The system according to claim 10,wherein the system is controlled to operate when the humidity within thestore is outside of a defined humidity range such that the humiditywithin the store is corrected to within the defined range.
 16. Thesystem according to claim 1, further comprising at least one heater. 17.The system according to claim 16, further comprising temperaturemonitoring means for monitoring the temperature within the duct.
 18. Thesystem according to claim 17, wherein when the system is operated andthe temperature within the duct is below a set duct temperature theheater is operated to thereby raise the temperature within the duct. 19.The system according to claim 16, further comprising temperaturemonitoring means for monitoring the temperature within the store. 20.The system according to claim 18, wherein the temperature monitoringmeans for monitoring the temperature within the store comprises aplurality of temperature probes positioned within the perishable goodswithin the store.
 21. The system according to either claim 19, whereinthe system, including the at least one heater, are controlled to operateand thereby raise the temperature of the air within the store when thetemperature within the store is below a defined store temperature. 22.The system according to claim 1, further comprising data storage meansfor recording data from the monitoring means and for recording when andhow the components of the system are operated.
 23. The system accordingto claim 1, further comprising a plurality of exhaust means locatedaround the store for controlling the exhaust of air from the store suchthat when the system is in use the volume of air being drawn into thestore is substantially equal to the volume of air leaving the store. 24.The system according to claim 23, wherein the exhaust means compriseexhaust louvers.
 25. The system according to claim 23, wherein theexhaust means are automatically controlled by the controller.
 26. Amethod of operating a ventilation system of a perishable goods storecomprising a duct through which air is propelled into the store, whereinthe air pressure within the duct is monitored and pressure control meansare used to control the pressure within the duct such that it remainswithin a defined pressure range.
 27. A The method according to claim 26,wherein the air speed through the perishable goods is monitored and whenthe system is operated it is controlled to provide at least a minimumair speed through the goods.